1981 MusicMan 75 Head 2100

Repair Log: 1981 MusicMan 75 Head 2100 – 75 EX SN: xxxxxxx

23/06/18 Copyright retained Terry Relph-Knight

RRP in 1980 $445 Value today – £ 200

Supplied with a 1M Fender speaker jack cable.

This MusicMan head is a hybrid transistor / valve design, rated at 75 Watts r.m.s. !! from a pair of 6L6GC output valves (it currently has a pair of JJ’s).

The B+ voltage must be very high (yup it’s 700Volts, the JJ 6L6GC is rated at 500Volts maximum). 

This would seem to be pushing what can be achieved from a push-pull pair of 6L6GC, which are rated at 30Watts maximum anode dissipation each, to almost insane levels. It is set for 220Volt mains, which probably means it is over-volting even further. Power rectification is of course solid state.

Like apparently all Music Man amplifiers this amp can be switched to low power or (75 Watts) high power on the three way Standby switch, which is standby in the middle, up for Hi power and down for Lo power. This is done by switching between two voltages for B+. Hi power is 700volts and Lo is 350volts. Actual measurements into an 8 ohm resistive load show 63Watts and 30.25Watts, so no you can’t squeeze 75Watts out of a pair of 6L6GCs and Lo power is half the high power output

The pre-amp is entirely solid state. It has two channels – Normal and Bass. Each channel has two inputs – 1 and 2 with 2 being -6dB quieter than 1. Both channels have a Bright/Normal rocker switch and Volume, Treble, Middle and Bass controls. The Bass channel has in addition a Master volume and a Deep/Normal rocker switch.

 1981 MusicMan 75 Head 2100 – 75 EX Repair Log

According to the dscription on the Reverb site this design is intended to provide good clean tones with a little added warmth from the push-pull valve output stage. However the circuit shows it has a master volume mixing stage that has back to back transistor / diode pairs in the feedback loop of an op-amp, which looks very much like a distortion circuit to me. This model was manufactured from 1980 to 1984. It uses a mix of op-amps (LF353 or TL072 in the pre-amp) and transistors right up to the the output valves. The push-pull output circuit has a pair of identical JE1692 transistors driving signal into the cathodes of the output valves, preceded by two op amps (dual op-amp LM1458) one of which provides signal to drive one transistor, and the other a phase inverted version to drive the other transistor. There is an internal adjustable bias control which sets the output valve idle current via the two cathode drive transistors. All four op-amps are fitted in sockets.

The inputs to this amp are quite low impedance, around 300K, rather than the ‘standard’ for guitar amplifiers of 1Megohm. Each channel uses one half of a dual op-amp as a pre-amp before a ‘classic’ passive tone stack. The second half of the op-amp buffers the tone stack. A dual gang channel volume has one half in the feedback loop of the input amp, controlling it’s gain and the second half as a passive volume on the output of the tone stack buffer with the buffer driving the wiper of the passive volume.

The outputs from the tops of the two passive channel volumes drive the input of a single op-amp stage that appears to be configured as some kind of distortion stage with transistor / diode pairs in its feedback loop. The output from this drives the top of a master volume and the wiper drives the input of a two op-amp phase splitter for the power amp.  The two outputs from the splitter drive common emitter NPN transistor stages, each of which drives the cathode of an output valve. The suppressor grids of the pair of 6L6 pentodes are both connected to the 350 volt rail via 470 ohm resistors and the control grids are both connected to a +22 volt rail via 220 ohm resistors. The anodes drive either side of the centre tapped primary of the output transformer. 

Problems – The output valves have been replaced with new JJs without re-biasing. The Bass channel hardly passes any signal (it’s possible that corrosion on the op-amp pins and socket has caused loss of contact). Amp is quite dirty and has some rusty bits. Looks like it was left standing in a shallow pool of water for a while.

Work done

Output stage biasing checked and re-set. Replaced the dead TL072 dual op-amp in the Bass channel. Cleaned the cabinet, knobs and the amplifier front panel. Much of the original knob numbering had worn away so I rubbed white wax into the knob engraving to improve the visibility of the numbers. Tightened several loose nuts on the controls. Measured the output into a resistive load while observing the output on an oscilloscope for power measurement, purity and clipping point.

Diagnosis –

The cabinet of this amp is quite dirty and various metal parts are quite rusty, with some rust on the transformer laminations! It looks as though the amp may have been left sitting in a shallow puddle for a while. The chassis is a welded steel tray with an angled front for the controls, suspended upside down in the cabinet from four long bolts in the four corners in the fashion of all the old Fender amplifiers. Getting the fourth nut, which is tucked behind the power transformer, into place on the thread of the bolt is an absolute PIA!! 

Hand written on the pre-amp PCB is – BC 1/12/81. Assuming the American convention of month/day/year this probably means the amplifier was assembled or final tested on the 12th of January 1981. The chassis has a paper self adhesive label 81-4.

Since the dead ‘Bass’ channel has a dual TL072 op-amp as the main active component and the op-amps are socketed, the easiest thing to do, rather than poke around measuring things, was to try replacing the op-amp. Seems to have worked.

An online source says this about bias


A. This applies to all models containing the following circuit boards:

DB-2, DB-3, DB-4, GP-1, GP-2, GP-3, GP-3A,GD-1,GD-2 AND GD-2A.

B. Adjustment is as follows:

1. Turn the amplifier to “ON” with the HI / LO Standby switch in the HI

position. No Signal.

2. Using a voltmeter measure the voltage from emitter to ground on each of

of the two driver transistors. Across the 3.9 OHM emitter resistors is a

convenient measuring point.

3. Adjust the bias trimpot (TR-1) until you read 25mv DC across the 3.9

OHM emitter resistors. If there is a difference in voltage between the

emitters of the two driver transistors, set the lower of the two to 25mv.

The higher of the two should not exceed 55mv DC. 

Voltage across the 390 ohm nearest the back panel is 16.4mV and 14.4mV across the in-board (which at some point had burnt out and has been replaced by two 680 ohm).

Reset to 25.7mV and 24.3mV. Remeasured 28.9mV and 28.1mV. 

Voltage on either side of the Standby / output power switch is 242.5V and 362.2, basically the voltage is the same on either side and it changes as the switch is flipped ???? Hmm, seems there is some odd voltage doubling circuitry. The actual B+ to the red wire on the output transformer does what it is supposed to. Pin 3 (anode) on the output valves flips between 483volts and 722volts as the switch is thrown.

The amplifier is set for 220V mains so yes the B+ will be even higher than the specified 700V.

Output transformer primary has a red wire to B+ a blue to the anode of V2 and a brown to the anode of V1 (V1 is the valve nearest the end of the chassis, anodes of 6L6GC are pin 3).

Red to Blue = 212.4 ohms, 1.207 on Hi     Red to brown = 191.0 ohms, 0.99volts on Hi

Red to ground = 726volts Hi, 485 Lo

Anode current V1 = 1.207/212.4 = 0.005682674 amps = 4.1Watts dissipation  !? doesn’t seem right

Anode current V2 = 0.99/191 =  0.005183246 amps = 3.758 Watts dissipation

Output power tests

Standby switch up Hi power measured output into 8 ohms = 63 volts p-p = 63 Watts r.m.s.

Standby switch  down Lo power measured output into 8 ohms = 44 volts p-p =  30.25 Watts r.m.s.

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1981 MusicMan 75 Head 2100

Repair Log: 1981 MusicMan 75 Head 2100 – 75 EX SN: xxxxxxx 23/06/18 Copyright retained Terry Relph-Knight RRP in 1980 $445 Value today - £ 200 Supplied with a 1M Fender speaker jack cable. This MusicMan head is a hybrid transistor / valve design, rated at 75...

Guitar Lessons in Whetstone Guitar Lessons Whetstone believes that music is a powerful influence in everyone’s life. Our Mission is to provide our fantastic students with a great musical experience that leads to personal enrichment that will stay with them throughout their...

Mark Knopfler Sultans of Swing

Mastering the Pentatonic Article 4 - Mark Knopfler; “Sultans of Swing”, adding the 2nd, and flirting with Harmonic Minor. The Pentatonic Scale is the...

1988 Black Gibson 335 semi-hollow electric guitar

Repair Log: 1988 Black Gibson 335 semi-hollow electric guitar SN Repair Log: 1988 Black Gibson 335 semi-hollow electric guitar SN: xxxxxxxx   23/06/18 Copyright retained Terry Relph-Knight Supplied in a tan Gibson hard case. Made in the Gibson...

Why middle C

Why middle C? By Terry Relph-Knight, copyright retained 03/06/18 Most people will have heard of middle C, but apart from knowing it is a musical note somewhere around the middle of the piano keyboard, won’t know it’s significance. Why C? Why middle?

Mixolydian and the minor Pentatonic

Mixolydian and the minor Pentatonic When faced with improvising over a dominant seventh chord...

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Mark Knopfler Sultans of Swing

Mastering the Pentatonic

Article 4 – Mark Knopfler; “Sultans of Swing”, adding the 2nd, and flirting with Harmonic Minor.

The Pentatonic Scale is the holy grail for guitarists. It’s easy to play and it sounds amazing.

Mark Knopfler Mastering the Pentatonic

This series will show you how to get the most out of our favourite scale, and how making small modifications will get you sounding like the pros and their signature sound.

With any scale, it is important to learn the shape starting on the E string (like in previous articles) but also starting on the A string. This article will be using the D minor pentatonic at fret 5 on the A string (see right).

You will notice an extra note added in blue, this is the 2nd, a note Knopfler often uses in a trill with the minor 3rd (see in the licks below).

Achieving the signature Knopfler sound isn’t just about note section but also articulation and phrasing. You will very rarely (if ever) see Knopfler using a pick. He employs a “claw” technique between his thumb, first and second finger. This means he plays lines that you might not think up with a pick. This also leads to the heavy use of double stops; playing two notes at the same time, and rakes.

“Sultans of Swing” licks: 1. Intro

“Sultans of Swing” licks: 1. Intro

This opening lick perfectly shows the 3 main ingredients to Knopfler’s playing; the pentatonic scale, finger- style, and the use of the 2nd.

Bar 1 & 2 is made up of a classic pentatonic lick with lots of vibrato. Bar 3 has a “rake” in it from the G string to the E string, quintessentially Knopfler – assign a finger to each string and make it snappy! It’s also worth noting that these notes make up a D minor arpeggio and highlight the chord underneath perfectly, another Knopfler move. Finally we have a hammer-on-pull-off between the 2nd and m3 on the B string.

2. Verse double stops

Verse double stops


Here we see how Knopfler uses double stops. They reinforce the harmony but also act as a rhythmic device. The syncopated pattern help push these couples bars along. Play these using your 1st and 2nd finger, with the final triad being played with thumb, 1st and 2nd finger.

Below is a lick that is made up of all the ideas we have discussed so far.

Mark Knopfler Sultans of Swing


3. Verse Harmonic Minor use.

Although very much in D minor, “Sultans of Swing” throws in an A dominant 7 chord every now and again, a chord “outside” the key. If you were to play a D minor pentatonic over the A7, the C (m7) of the D minor pentatonic would clash with the C# (3rd) of the A7 chord. To get around this, Knopfler dips into a D Harmonic Minor scale, which is a D minor scale with a major 7th:

Verse Harmonic Minor

Mark Knopfler Sultans of Swing   PDF available. Get you GUITAR LESSONS LONDON here!

1988 Black Gibson 335 semi-hollow electric guitar

Repair Log: 1988 Black Gibson 335 semi-hollow electric guitar SN

Repair Log: 1988 Black Gibson 335 semi-hollow electric guitar SN: xxxxxxxx


23/06/18 Copyright retained Terry Relph-Knight

Supplied in a tan Gibson hard case.

Made in the Gibson Nashville Tennessee plant, completed on February 24th of 1988, this is a classic Gibson 335 thin line semi-hollow electric guitar in gloss black nitro-cellulose lacquer with nickel plated hardware. From the condition of the nickel plating and scuffing on the finish, the guitar shows signs of a fair amount of use, but considering its age it is in good condition and has been well cared for. 

From 1969 to 1986 Gibson was owned by the Norlin Corporation, so this is a post Norlin guitar from the early period of Juszkiewicz management. From 1986 Gibson has been a privately held company, owned by its chief executive officer Henry Juszkiewicz and its president David H. Berryman. In May 2018 the company filed for Chapter 11 bankruptcy protection.

Body of pressed maple/poplar/maple plywood with a maple centre block and a one piece mahogany neck with a 22 fret rosewood fretboard. Pearl dot fret markers. Fretboard shows some fingernail gouges in the first position and the medium frets appear to have recently been fret dressed, as there is little fret wear, the tops of the frets are quite flat and the fretboard is very clean for a guitar of this age.  

Repair Log: 1988 Black Gibson 335 semi-hollow electric guitar SN


Black Gibson 335

Hardware – Two humbucking pickups (should be old Classic ‘57s) with nickel plated shells. Now checked – externally these pickups look very similar, even the pole spacing is the same at 49.2mm. The pickups have nickel silver shells and base plates – stamped PAT. 2,737,842, no other markings. The serial is a known Gibson quirk. It isn’t the patent number for humbuckers, but actually the patent number for the old combined bridge and tailpiece found on the very earliest Les Paul goldtops. Since the pole spacing is the same, one has a coil tap and the embossed Pat. No. only marking was not introduced until 1990 (maybe), these may not be the original pickups. Perhaps a pair of 490Rs, with one modified with a coil tap.

Open bottom nickel plated cast zinc alloy Nashville bridge with metal saddles. The bridge has sagged in the middle by 0.8mm due to string pressure. Probably a zinc alloy stop bar. Grover 3-on-a-side nickel plated tuners.

The Volume control for the bridge pickup has been modified with a built-in pull-push switch, to switch a coil tap on the bridge pickup. This pot has an Asian 16 spline shaft. The other three pots are American and have 24 spline shafts. All four knobs are the original American 24 spline.

Gibson 335 semi-hollow electric guitar

As delivered, fitted with flat wound strings, gauges – 0.009, 0.014, 0.017, 0.023, 0.034, 0.046

Problems – Needs cleaning and a general check over. The pick guard threaded support rod is missing the outer nut and the plastic block the rod runs through, is no longer glued to the back of the pick guard. The retaining nut on the output jack is loose. Pickup selector switch nut is loose. Pot nuts are loose. Truss rod cover is broken at the nut end (52mm fixing centres). Two of the black UFO knobs are cracked and one does not fit the pull/push bridge Volume pot. Bridge is corroded and has some sag.

Work done – Guitar cleaned and polished. Polished all the metalwork. Repaired and reattached the pick guard and its mounting bracket. Tightened the loose output jack and pickup selector switch and painted clear nail varnish onto the fixing nuts and threads to lock them. Tightened various loose nuts and screws on the tuners. Fitted a Faber locking kit with spacers to the stop bar and fitted a Tone Pros locking bridge. Dug lumps of nitro- cellulose lacquer out of the truss rod route so there is clear access to the truss rod nut. Removed the truss rod nut, cleaned off blobs of nitro-cellulose lacquer and filed off burrs from previous attempts to adjust it. Put some lubricating grease on the threads and replaced the nut on the truss rod. Replaced the broken truss rod cover, the cracked control knobs and the broken pickup rings. Cleaned, waxed and buffed the fretboard and frets. Fitted a new set of 10 to 47 round wound strings, adjusted the set up and intonation.


The floating pick guard support is missing the acorn nut and the threaded plastic block the support rod threads into has come unglued from the pick guard.  The outer diameter of the threaded portion of the pick guard support rod is 0.12 inches. This is equivalent to a number 5 thread. If it is a UNC thread then there will be 40 threads per inch as against 44 tpi for UNF. Most likely it is a 5-40 thread. So I need a 5-40 Acorn or blind nut. Replacement UNC 5-40 acorn nuts or even 5-40 nuts are almost impossible to source. Eventually I took a 4 B.A. nut, which was a loose screw fit on the rod, and soldered it onto the end of the rod.

As it turns out this pick guard would never have fitted properly with this old style threaded rod support. When the vertical post is screwed to the outer rim of the guitar the pick guard rides up on the inner nut of the threaded rod. As a result the pick guard has to bend for the threaded plastic block that is glued to the back of the pick guard to thread on to the rod. This puts unnecessary pressure on the glue joint between the plastic block and the pick guard and eventually the joint fails.

There are two solutions – re-shape the outer edge of the pick guard so it clears the nut, or cut a notch in the edge of the guard to clear the nut. Re-shaping by hand would be a lot of work so I opted to notch the guard. Refitted the guard and re-glued the guard to the plastic block with super glue. This may not hold on the back of the vinyl guard, but it seems fairly solid so far. 

Intonation as delivered with the flatwounds

cents error

E -12

A -3

D -6

G -4

B 0

E +5

Set up as delivered – The stop bar is screwed all the way down and the two E strings are touching the back of the bridge.

The bridge from the top of the guitar to the top of the thumb wheel is at 7.5 mm on the bass side and at 5.75mm on the treble.

Open string height at the twelfth fret – top of fret to bottom of string – is 2mm on the bass, 1.6mm treble. Relief with low E fretted at 1 and 12 is around 0.5mm.

All the electronics seem to be functioning correctly. Unscrewed the two pickups for cleaning and to check the back. The bridge pickup has been rewired for the coil tap with a grey cable. Neck pickup ring is broken – top high E corner.

From the front with the strings on all six tuners seemed secure and the front collar nuts seemed tight, however with the strings off and holding each of the tuner buttons I could waggle the tuners on the low E and the D, G and B strings. Either the tuners move back and forth on their rear screws or the button tension screws are loose and therefore the gear trains are loose, or both. The D and G had particularly loose gears. Any movement in the tuners will affect the tuning stability of the guitar.

Removed the truss rod nut to lubricate it. Looks like an attempt has been made to adjust it with the wrong tool. There is some damage on the flats of the hex nut.

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Why middle C?

Why middle C?

By Terry Relph-Knight, copyright retained 03/06/18

Most people will have heard of middle C, but apart from knowing it is a musical note somewhere around the middle of the piano keyboard, won’t know it’s significance. Why C? Why middle? 

Guido the Monk

The existence of western musical notation and consequently middle C, is due to the Catholic Church seeking uniformity in church worship. The church leaders were concerned about heresy, they wanted to be sure that wherever Christianity was practised, everyone followed the same dogma; they believed the same things and all worshipped in the same way. In the 10th century, plainsong or plain chant – unaccompanied singing performed by monks and boys – was a part of religious services. The problem was there was no accurate system of writing music. All they had was a series of marks or neumes above the written words of the chant. This did little more than indicate that the next note went up or down in pitch and provided some idea of the articulation. Chants had to be memorized and could only be taught directly from one person to another. There was always the possibility for mistakes to creep in, or for music to be lost altogether.

Why middle C ?

A musical theorist, a monk known as Guido of Arrezo or sometime just Guido Monaco (the monk), solved the church’s problem by inventing the basis of western musical notation.

He took the neumatic notation and extended it into a five line staff or stave. Five lines are a small, easily drawn and read number. Notes are written either between, or on the lines, and by placing the bottom note in a sequence just above the bottom line, then counting all the spaces and lines and ending immediately above the fourth line, you get seven notes. The eighth note in the sequence is of course the octave, so a five line staff can comfortably cover one octave. To cover wider ranges of pitch, further sets of five staff lines can be used and short extension ledger lines can be drawn above or below the five line staff. Each staff is separated by at least a single ledger line which isn’t drawn as a continuous line, leaving space between staves for the purpose of legibility.

Guido based his system on the pitch range of the male human voice. The overall pitch of a five line staff is indicated by a clef sign (clef from the French, meaning key) at the beginning and Guido started with two pitch ranges of bass and treble. He used the letters of the Roman alphabet to name the notes and he chose to start with A in the gap between the bottom line of the bass clef and the next line up. He then carried on naming the seven notes of the major scale in alphabetic order, as B, C, D and so on, ending on the seventh as G just below the top line. The next note is the octave A, the same as the starting note only twice the frequency, and the seven letter sequence repeats. 

So, despite the modern practice of referring to a C to C octave, the note sequence originally started logically with the letter A, not C. For tuning purposes the reference note is usually an A. The frequency of this reference note has varied over time. Only relatively recently in the early 1900’s has orchestral pitch settled (more or less) on an A of 440Hz which puts ‘middle’ C at 261.63Hz (Hertz or Hz is cycles per second in old money).

Guido was creating musical theory in the 10th century to suite the church music of the time. This was modal music based on six note hexachords. Now a thousand years later musical complexity and musical taste have changed and the C major scale, the only major scale with no sharps or flats, is central to Western music. The C to C major scale organisation of the white keys on the piano, an instrument not even thought about in Guido’s time, along with the five black keys, is an easily recognised pattern and the piano keyboard is often used as a reference. If we were to re-write musical theory and the method of musical notation today, we might choose to re-label the notes.

The Grand Stave


The Grand Stave

The Grand Stave

The Grand Stave covers a span of three octaves, with the treble clef above the bass clef, divided by the single ledger line occupied by Middle C

If you stack a treble stave above a bass stave you get two sets of five lines separated, for clarity, by a single ledger line (and a space above and below it). Although never used in written music this is known as a grand stave or staff. Following the Guido system, starting with A in the bass clef you will find the note letter that sits on that central ledger line is a C. This is where middle C comes from, for the grand stave it is the central note between the bass and the treble staves. 

The bass clef symbol is a stylised letter F with the two dots split by the stave line for the note labelled F and the treble clef symbol is a stylised letter G with the centre curl of the letter on the stave line for G.

The Grand Stave covers a range of three octaves. A good fit for the range of the average human voice, which is around three and a third octaves. The range of many instruments doesn’t extend much further, although their overall pitch may be higher or lower. 

In written music with treble and bass staves the two are written spaced apart and high notes in the bass or low notes in the treble are given their own short ledger lines, rather than migrating across from one stave to the other. Multiple ledger lines are often used, but beyond four or five ledger lines the notation becomes hard to read and at this point the notation may switch staves. The assumption is that the treble and bass parts will be performed on different instruments and music is more easily read if the parts are separated. Instruments such as the piano, that can span across the bass and treble, still have the parts written on separated staves because the left hand plays the bass and the right the treble.

Written guitar music

It is a curious fact that the modern guitars pitch range places it in the bass clef, but guitar music is usually written an octave higher in the treble stave. This can cause problems for session guitarists expected to play from a score written by a composer that doesn’t know the real pitch of the guitar. The F of the bass clef is normally pitched at 174.61Hz. The low E of the guitar is the second E below that, at 82.41Hz, located on the first ledger line below the bass stave.

There are other clef symbols than the treble and bass G and F clef’s. For example the alto clef, which is well suited for the pitch range of cello music and as it happens, guitar. And the tenor clef. In total there are ten clefs that have been used in musical notation. However these ‘specialist’ clef’s are rarely used, it’s just simpler to use the treble and bass clef’s and transpose parts to fit.

The reason for this pitching oddity is that early guitars, like many string instruments even today, had only four strings (or more accurately – four courses of two strings each). The name “guitar” derives from the Old Persian “chartar”, which literally means “four strings”. Many four string instruments, like the violin, are often played in ensemble and rather than having strings added to expand the range, are part of a family of instruments. For the viol family we have, roughly speaking, the violin, the viola, the cello and the double bass. Both the Cremonese old masters – Amati, Stradivari and Guarneri del Gesu – and modern makers have supplemented this range with other sizes of instrument. Traditionally the viol family is used classical orchestras and the frequency range is expanded by the use of different sizes of the basic instrument design. In comparison the guitar is not considered an orchestral instrument, rather it is an instrument that is often played on its own, or in small groups. Although we do have the bass guitar and the rarely seen, short scale Terz guitar. The four string tenor guitar doesn’t really count as part of the guitar ‘family’ because it is really a banjo with a guitar body.

Over the years, just as with the lute, which started life as a four string instrument, composers and players sought to extend the range of the guitar and it acquired a fifth bass string and then a sixth. This is one of the things which makes the guitar a special instrument, these extra strings make it possible to play a bass line, rhythmic chord patterns and melody lines all at the same time. Altered tunings extend these possibilities even further. It is quite natural to down tune the two bass strings and play a bass line on those, with the top four strings for chords and melody.

As to why western music uses seven notes for a major scale and eleven notes including sharps and flats (or 8 notes and 12 notes if you include the octave) is a question for a another time.

Mixolydian and the minor Pentatonic

Mixolydian and the minor Pentatonic

When faced with improvising over a dominant seventh chord or a progression of dom7’s, many guitar players tend to resort to the minor or the Blues pentatonic as their default tonal material. Especially in a “bluesy” context, such as a standard Blues progression, this works very well and the straight forward structure of the pentatonic allows plenty of room to think about phrasing, timing, tone and all the other musical parameters that go beyond harmonic material.
However, integrating the Mixolydian scale into your harmonic repertoire will add a whole new musical component to your solo playing and, especially in combination with the minor pentatonic, can make your solos sound a lot more exciting and engaging to the listener!

Constructing the Mixolydian scale

Mixolydian is the fifth mode of the Ionian system. This means that if you’ll play the Ionian (major) scale from its fifth note onwards – thinking of that fifth note as the new root – you will end up with a Mixolydian scale.

Take for example C Ionian ( C D E F G A B C ) and play it from its fifth note G onwards, up to the next G – this will give you G Mixolydian ( G A B C D E F G). The numbers above the tab below tell you which degree of the scale each note represents:

C Ionian

C Ionian

C Ionian

G Mixolydian

G Mixolydian

G Mixolydian


If you’d like to read more about the Ionian System and its modes, have a look here:


For the most part, the Mixolydian scale is identical to the Ionian scale, except for one crucial detail: While Ionian has a major 7, Mixolydian has a minor 7, making it the perfect scale for Dom7 chords, which – just as the Mixolydian scale – contain a major third and minor seventh.

So, another easy way of constructing Mixolydian scales is taking a major scale and simply lowering its seventh note by a semitone. In the following examples, we’ll expand the scales over several octaves covering all six strings to give you a practically useful pattern for each scale.

C Ionian


C Mixolydian

C Mixolydian

C Mixolydian

Note that the difference between C Ionian and C Mixolydian is their seventh note (B and Bb).

Combining Mixolydian and the minor pentatonic

As mentioned earlier on, a strong way of incorporating the Mixolydian scale into your solo is combining it with the minor pentatonic, as this brings out the characteristics of each scale. Let’s have a look at which notes the two scales have in common and which notes make up the differences:

C minor pentatonic

C Eb F G Bb C

C Mixolydian

C D E F G A Bb C

The main difference – apart from the obviously different amount of notes that each scale is made up off – is the major third in Mixolydian opposed to the minor third in the minor pentatonic. This minor third played on a Dom7 chord (which itself inherently has a major third) is what makes it sound “bluesy” and somewhat wailing, and is an important stylistic device in Blues improvisation. Using the major third of Mixolydian will give you a brighter sound, bringing out a different shade of the Dom7 chord you’re improvising on. The major second and sixth of Mixolydian further add to that brighter sound, the rest of the notes (1 4 5 7) are identical to the pentatonic. In the following example on a C7 chord we’ll combine the two scales – note how the feel gets brighter once we switch to Mixolydian in bar 3 (not counting the pick up bar)!



Every Dom7 chord has its own respective Mixolydian scale. When the chord changes from C7 to F7 in our Blues progression, the Mixolydian scale of the moment would now change to F Mixolydian as well.
A strong way of navigating through those chord changes without “merely” jumping from one Mixolydian to the next, is to alternate between the minor pentatonic of the key (C min pent) and the Mixolydian scale of the moment (C, F or G Mixolydian).

A great exercise to practise this is to write out the chord progression your are improvising on and to mark in which tonal material you’ll use in your solo at what point. An example could look like this:

Mixolydian and the minor Pentatonic



As you can see, there are almost endless possibilities of when to use which scale and it is great practice and a lot of fun to experiment with different combination of those scales and to listen to how the sound and feel of your solo changes!

The Mixolydian Pentatonic

At the end of this article, I’d like to show you hybrid between the minor pentatonic and the Mixolydian scale: The Mixolydian Pentatonic, which just as the minor pentatonic (and every other pentatonic for that matter – that’s why they call it pentatonic) consists of five notes. We can easily construct that scale by simply turning the minor third of the minor pentatonic into a major third:













The Mixolydian Pentatonic

The Mixolydian Pentatonic

This scale contains the “essence” of the Mixolydian sound and, due to its structural similarity to the minor pentatonic, is a great gateway from the minor pentatonic towards the Mixolydian scale!

Article 3 – Mixolydian and the Minor Pentatonic


Repair Log – 2005 Laney VC30-112, 30 Watt ‘class A’ combo 1 by 12 guitar amplifier Serial no JVxxxx. 

23/03/17 Copyright reserved Terry Relph-Knight

Value – As is, maybe – £ 300,  £480 to 500 (inc postage) new 


The Laney VC30 is now a discontinued product. It is Laney’s version of the Vox AC30 configuration. Another model, the VC30-212, featured a larger cabinet with two 12 inch loudspeakers, just like the Vox. The Laney VC30 amplifier also appeared with a flat baffle and an HH loudspeaker, where the large magnet was so close to the valves that the magnetic field interfered with correct operation and caused red plating. Other versions with an HH loudspeaker, but mounted on a sloping recessed front panel, are apparently OK because the magnet is further away from the valves.

REPAIR LOG – 2005 LANEY VC30-112

REPAIR LOG – 2005 LANEY VC30-112

The Laney VC30-112 combo uses four EL84’s (TAD STR Selected S1’s) with no negative feedback around the power amplifier, running in ‘class A’ to produce 30Watts into a single 12 inch loudspeaker. The amp is fitted with a single Celestion Seventy 80 G12P-80 8ohm loudspeaker. The Laney tech department tell me the amplifier in for repair is 12 years old.

The VC30 has an Accutronics 16 ¾ inch, four spring (a pair of 2 springs in series) reverb tank. The tank output should be oriented at the power switch end of the amplifier to avoid feedback and connected to the red phono on the PCB. The white phono is the drive to the input of the tank. The amp has an FX loop for external effects and an external dual foot switch can be used to switch the reverb on and off and to switch between clean and drive. The Reverb level control runs directly into the power amp input and the reverb is in parallel with the effects loop.

This is a two channel amp with a clean and an over driven channel. Switched to the over driven channel with the Drive and Drive Volume at maximum there seems to be a ridiculous amount of gain and therefore quite a high level of noise from the input valve.

Valve complement – 3 x 12AX7, 4 x EL84, the two pre-amp valves and the four output valves appear original and are TAD brand. The phase splitter has a different appearance and no surviving brand or type markings (the Laney VC30 manual confirms that all three pre-amp valves are ECC83 / 12AX7s, so the phase splitter is not a different dual triode. The first 12AX7 is described as needing to be a ‘high grade’ by which they likely mean low noise, low microphonic’s).

Laney VC30 rear

Laney VC30 rear

The EL84s all have retaining clips (the retainers on output valve 2 and 4 have snapped in half) and the 12AX7s have sprung screening cans.

Laney number these valves as V1,V2,V3 (all 12AX7),V4,V5,V6 and V7 (all EL84) from right to left looking at the back of the amplifier.

Front panel controls – Input Lo, Input Hi, Clean Volume, Bright switch, Drive, Drive Volume, Drive switch, Drive LED, Bass, Middle, Treble, Reverb, FX Level (on some versions this was an extra tone control), Standby switch, Power Switch, Power LED. The front panel is mirror polished stainless steel with the control labels silk-screened in black, Unfortunately some of the silk-screening has started to flake away. Personally I do not see how any form of silk-screen printing can be expected to stick to a highly polished metal surface, but Laney say that these panels were printed with a 2 pack epoxy ink and that therefore ‘it is impossible’ for the lettering to just flake off (obviously, they are wrong).

NOTE – The tone control design on this amp is the configuration that passes no signal if all three tone stack control are set fully anti-clockwise.

Back Panel – IEC 3 pin fused mains socket, 20mm HT fuse, Internal ‘cabinet’ (loudspeaker) jack, 8ohm / 4ohm output impedance switch, FX Return jack, FX Send jack and Drive/ Reverb foot-switch jack.

A rather poor feature of the construction of this amplifier is the use of ¼ inch smooth shaft, grub-screw chicken head knobs fitted to 6mm, split shaft, knurled controls. Since the the knobs don’t fit properly they tend to fall off, or spin uselessly.

Another dumb thing, common to all Laney amplifiers, is having the internal loudspeaker cable threaded through one of the square perforations in the rear protective grille. Which means you cannot unscrew the grille and remove it completely, to get it out of the way during repairs, because it remains tethered to the amplifier by the loudspeaker cable. I cut out one side of the perforation so now the grille can easily be removed and replaced.

The original strap handle on the top of this amplifier has been removed and replaced, rather sloppily, with a larger handle. The new handle has been mounted with mismatched screws, off centre and at an angle. Apart from the problem with the handle, the flaking control labelling on the front panel, the burnt out output valves, the broken valve retainers, knobs that don’t fit the control shafts, a 230V power supply that runs HT and heaters way over the maximum specification and the chassis retaining screws that are too short, this amplifier is in very good condition.

Problems – Amplifier crackles after being left on for a while. There is also a lot of hum from the loudspeaker. Two of the EL84 spring retainer clips snapped in half while I was removing the output valves. Carrying handle has been replaced with a poorly mounted, off centre handle, held on with mismatched wood screws. The 6 bolts that hold the amplifier chassis in place aren’t long enough and only barely engage with the cage nuts on the chassis. In fact only 4 bolts can engage with the nuts. As usual with Laney the internal loudspeaker cable is threaded through the rear protective grille because they were too lazy to cut a notch in it.

Just about to ship the amplifier out of the door when I find there is a problem with the heaters not working on the (2nd set off replacements) output valve nearest the mains transformer (blown heater filament connection).

Oh for crying out loud!! Fitted the heater voltage dropping diodes and the four Electro Harmonix EL84s supplied by client and about to declare the repair done when I find that with the Reverb level at around 5 (all other knobs at zero) the reverb tank feeds back at around A 220Hz. 

Work done – Replaced the set of four matched TAD EL84 output tubes with a set of four matched JJ low dissipation EL84, Plate current 47.1mA, Transconductance 10. Output valves still red-plated so increased the cathode bias resistor from 56 to 68 ohms. I still had a red plating problem on one of the four valves so I returned the valves to Hot Rox for re-testing. 05/05/17 Received a replacement set of EL84’s PC 38.1, TC 9.7 from Hot Rox. These don’t red plate, however the heaters on one of the JJ EL84 exhibited a bright heater flare where one end of the filament was welded to the pins. After a short period of testing one end of the heater filament disconnected from the weld to the pin in the valve base. 

Eventually fitted two pairs of 6amp rated, back-to-back diodes mounted on a tag panel to drop the heater voltage down to something that won’t fry the valve heaters. The TAD EL84 data sheet gives the max and min ratings for the heater voltage as 6.8 to 5.8 volts. The measured heater voltage with the old set of TAD EL84s was 7.88V AC !!

Replaced all EL84s with a matched set of Electro Harmonix supplied by Folkies. Also replaced the first 12AX7 in the pre-amp which was very noisy and crackly.

Hum is much reduced. Replaced the broken valve retainer clips. I removed the poorly mounted handle, measured and drilled holes and refitted the handle with a pair of 5mm bolts. Tightened loose nuts on the two loudspeaker jacks. Added card inserts into the slots in the eight bifurcated control shafts in an attempt to stop the shaft closing up under pressure of the knob grub screws, with the knob loosening or falling off as a result. Cleaned a lot of dirt from the back side of the PCB.

Amplifier wiped clean on the outside and vacuumed inside to remove dust.

Reverb feedback problem – tried reversing the reverb tank in the cabinet. Feedback problem solved, even with the Reverb level at maximum – no feedback.

Oh… and … the six bolts that are supposed to hold the chassis into the cabinet by engaging with cage nuts, are just that little bit too short. You are lucky if you can even get a couple of turns of thread to engage and even then you cannot get all six bolts into all six nuts because the chassis is about 3mm narrower than the cabinet !!!!

I replaced the two bolts on input side of the cabinet with two M5 30mm. DO NOT put these bolts anywhere else they may short out the electronics in other positions.

Rather too many instances of shoddy, thrown together stuff that doesn’t quite fit on this amp if you ask me. Screwed up handle (probably an owner fix, although in that case the original handle likely failed as it was only held on with wood screws), silk screen labels flaking off the front panel, ¼ inch knobs that don’t fit 6mm knurled pot shafts, loudspeaker cable ‘trapped’ in rear mesh, bolts that are supposed to hold the chassis into the cabinet that are too short. Over high voltages from the power supply because the amp is designed for 230V AC and has no adjustment for real UK mains voltage (the power transformer also seems designed for and expectation of lower than 230V so the actual output voltages on real 240V are way over stressing the valves). And a reverb tank fitted the “wrong way round” that tended to feed back. 

A note on class ‘A amplifiers’

Most guitar amplifiers with a push-pull output stage operate in class B or class A/B. The Laney VC30, like the Vox AC30, runs the output stage in ‘class A’. This puts a lot of stress on the four output valves because, unlike most guitar amplifiers which idle the output valves at a lower power, the output valves in a class A design are biased to run flat out all the time. It’s a bit of a juggling act to design the output stage so that the valves are operated just at, or just below, their operating maximums. This is not helped by the fact that due to European Union legislation, most modern guitar amplifiers are designed to run on 230V mains. The mains voltage at most places in the UK is still 240V or higher. As a result the HT voltages (and heater voltages) for these valves amps run high. The HT is perhaps 20V higher than they were designed for. When you run a class A amplifier, already designed to run the output valves at close to maximum, with a higher HT voltage you are asking for trouble and heater voltages that exceed the specified maximum will cause the heaters to fail (Laney say otherwise on both counts).

There may also be variations between different valve brands in the degree to which they will withstand operation at or past their maximum ratings. In general, Class A amplifiers are likely to require their output valves be changed more frequently.


Once the back grille was removed is was clear to see that, after the amplifier has been left on for while, the leftmost two EL84’s (viewed from the back of the amplifier) are red plating, so they are obviously passing too much current. This could mean that either the grid resistors or connections are bad, or that the output transformer has a short (transformer checks out OK). The odd crackling and popping noises are probably due to the overheating valves momentarily shorting internally – (it later turns out the first 12AX7 was in poor shape and making horrible noises).

Output transformer primary is Blue – Black CT – Red. Blue to Black 36.3 ohms, and Red to Black 38.4 ohms. It’s the blue side pair of valves that are red plating which do have the lower resistance half of the winding.


Pin 1 Internal connection  82ohm to pin 9

Pin 2 Grid 1 1K5 to pin 6

Pin 3  Cathode and Grid 3

Pin 4 Filament

Pin 5 Filament

Pin 6 Internal connection 1K5 from pin 2

Pin 7 Anode

Pin 8 Internal connection – the internal connections on the TAD valves really don’t go anywhere

Pin 9 Grid 2 82ohm from pin 1

NOTE 1 – Laney have used pins 1 and pin 6 as support points for the control and screen grid 1.5K and 82 ohm resistor connections. THIS CAN BE DANGEROUS. These pins are marked as ‘Internal connection’ on many data sheets. Most new production valves have nothing internally connected to these pins. However some valves, particularly NOS, DO HAVE connections, for example Pin 1 is connected to Pin 2, the control grid. Damage will occur if valves that do have internal connections are plugged in to this amplifier.  

NOTE 2 – Some versions of this amplifier are fitted with a single HH loudspeaker (with a ‘flat’ baffle, sloping baffle version is OK). The magnet on these sits very close to the output valves. Close enough that the magnetic field from the loudspeaker influences the performance of the valves, causing low output power and early failure. Looking at the back of the amp the EL84 second from the right is the worst affected. Later versions of this amplifier use a Celestion Seventy 80 loudspeaker with a smaller magnet and are apparently not as badly affected (might still be a long term problem?).

According to the circuit diagram, all four output valves are cathode biased at 9V with a common 56ohm 5Watt resistor to ground (measures 10.7V). Combined cathode current at 9V would be 160mA or 40mA per EL84. At 10.7V across the cathode bias resistor, current is 191mA or 47.74mA per valve. In single valve operation, Ia is rated at 48mA.

Why one half of the push pull, red-plates, is a bit of a mystery (as noted previously it may be because these valves are connected to the lower resistance half of the output transformer primary) because all the grid resistors and connections seem to check out. All grid stoppers on pins 1 measure around 1.5K and the common ends of those to ground measure 220K. All suppressor grid (pins 9) resistors measure 82 ohms and are connected to B+. Most likely this set of valves is simply worn out.

Transformer Red is 317.5V (38.4 ohms to the CT) and Blue is 315.5V (36.3 ohms to the CT). Black (B+) is 318.2V.

For convenience I have numbered the output valves from left to right looking at the back of the amplifier as 1,2,3 &4. The spring valve retainers on output valve 2 and 4 have snapped in half.

All four valves have brown spots on the inside of the glass envelope opposite the grid alignment hole in the anode, so it certainly looks like all four have been working hard for some time.

As an experiment I swapped 3 and 4 for 1 and 2 to see if the red plating followed the valves or stayed on the same half of the output transformer primary.

With the valves swapped the red plating follows 3 & 4. 3 & 4  are running about 250 degrees on the glass while (4 is the most visible red) 1 & 2 are at 215 degrees. The red plating is most visible on the side of the amp that faces outwards when mounted in the cabinet.

Unfortunately the amp still red-plates with a brand new set of JJ EL84s.

An LTSpice computer simulation of the output stage shows it performing exactly as the circuit diagram indicates. The voltage drop across the common cathode bias resistor is 9.26V and the total cathode current is 165.5mA.

Measurements with the old set of TAD output valves.

Heaters – 7.74V AC this is very high, nominal is 6.3V

After the addition of the back-to-back diodes the heaters receive 6.36V.

B+ 321V – circuit shows 290V

Suppressor grid common 308.3V – circuit shows 280V

Input grid common for blue pair 4.2V !!!! (it is the blue pair that are obviously red plating)

Input grid common for red pair 0.75V !!!!

Voltage across the cathode bias resistor starts around 10 and then slowly keeps on rising.

The high heater and supply voltages are because this amp is designed for 230V mains and is running on 240V actual UK mains.

The only reason I can see for DC voltages on the common grid drives is that the coupling caps from the phase splitter are leaking. Certainly the LTSpice simulation shows no volts on the grids. The caps in the Laney are dark blue 22nF 630V plastic film. The PCB is printed with 400V for those caps.

Tried disconnecting the 22nF coupling caps C12 and C14.

With the caps disconnected and the back of the PCB cleaned, the pair of EL84’s that drive the blue side of the output transformer still have 1.9 odd volts on the common grid connection where it would normally connect with the phase splitter coupling cap.

With all 4 EL84’s unplugged and power applied there is no voltage on either the common grid connections or across the cathode bias resistor.

With the 4 new JJ EL84s each common grid connection has perhaps 30mV and the cathode bias sees about 10.8V. However this voltage does seem to slowly rise. It does seem as though the old valves are trashed and the voltages apparent on the grids are caused by the bad valves.

However the cathode bias level is high and the valves still red plate. I shall try a 68 ohm cathode bias.

With a 68 ohm cathode resistor the cathode bias is 11.83V

B+ 326V – circuit shows 290V

Suppressor grid common 315.7V – circuit shows 280V

Input grid common for blue pair 30mV

Input grid common for red pair 56mV

Red voltage is 324V 

Blue voltage is 323V

Valve temperature is between 220 and 240 degrees. 

Red drop 3.01V (38.4 ohms) current = 0.078385417 Amps = 23.932 Watts for the red pair

Blue drop 2.56 (36.3 ohms) current = 0.070523416 Amps = 21.509 Watts for the blue pair


Red drop 3.111V (38.4 ohms) current =  0.081015625 Amps @ 311.9V drop across the valves =  25.268 Watts for the red pair (labelled 1 and 2 with silver marker)

Blue drop 2.571V (36.3 ohms) current =  0.070826446 Amps @ 312.3V drop across the valves =  22.119 Watts for the blue pair (labelled 3 and 4 with silver marker)

In an attempt to balanced the power of each pair I swapped 1 with 3.

Red drop 2.708V (38.4 ohms) current =  0.070520833 Amps @ 312.8V drop across the valves = 22.058 Watts for the red pair (labelled 3 and 2 with silver marker)

Blue drop 3.023V (36.3 ohms) current = 0.083278237 Amps @ 313.1V drop across the valves = 26.074  Watts for the blue pair (labelled 1 and 4 with silver marker)

Try 3,4,1,2

Red drop 2.705V (38.4 ohms) current =  0.070442708 Amps @ 307.7V drop across the valves = 21.675 Watts for the red pair (labelled 3 and 4 with silver marker)

Blue drop 2.938V (36.3 ohms) current =  0.080936639 Amps @ 307.5V drop across the valves = 24.88 Watts for the blue pair (labelled 1 and 2 with silver marker)

Re-tested with 230V AC mains set and supplied by Variac.

Even at 230V AC the second EL84 from the mains transformer still red plates. It has to be because the supposed matched set I purchased from Hot Rox just are not balanced.

05/05/17 Received a replacement set of EL84’s PC 38.1, TC 9.7 from Hot Rox.

29/08/17 Replaced output valves with a set of Electro Harmonix EL84s 

Valve temperature is around 220 to 190 degrees C.

Output power test

The amplifier develops 40.4 V peak to peak into an 8 ohm resistive load at 400Hz.

That’s 25.5 Watts.

I contacted Laney technical support about the red plating problem and this is what they said –

For the first 13 years of its life the VC30 had a HT of 320V and the were no problems encountered, this is a standard voltage for an amp of this type,

The voltages were lowered slightly due to power surges in Australia, as here the supply voltage is 240V, but their voltage does vary and can be as high as 260V, we had a few instances where the power fuse would blow for no apparent reason.

To rectify this we reduced the voltage and added a surge guard to the power supply, this does however come at a price and the output is reduced slightly below 30W output.

I do not think the transformer is a problem on your amp, but you are more than welcome to purchase a new transformer to try, another thing to check is the output tubes as we have seen matched sets that were very poorly matched.

 We can supply a new transformer for £46.99 shipped to a UK address.


Dave Thompson

UK Service & Production Supervisor

Parts – 2 x replacement valve clips £4, 4 x P600A 6A diodes £1.56, tag panel £1.0, spacers £0.50, bolts £2.50, 68ohm 5W wire wound resistor £0.50, JJ 12AX7 £13.00, 2 x Electro Harmonix 12AX7s £ 25.95

Total parts – £ 49.01

Repair Log: 1965 Epiphone Olympic Special (looks like a Gibson Melody Maker) SN:xxxxxx

Copyright reserved T Relph-Knight 19/09/17

Value – £750 to 800? although Reverb lists 1965s of this model @ £916, or in excellent condition (still showing a few chips and dings around the edges of the body and at the headstock) @ £1,453.

The New Kings Road Vintage Guitar Emporium UK listed a 1964 Epiphone Olympic (with a sprung steel Vibrola vibrato) for £1,115 in January of this year.

Weight – 2.7 kg 5.95 lbs

A quite heavily worn, double cutaway, Epiphone Olympic Special. The Olympic Special was introduced in 1962 and discontinued in 1970. The asymmetrical body with the bass horn slightly longer than the treble was introduced in 1965. The guitars serial number does not show a hit on the Epiphone serial number database. states that Gibson made, Epiphone serials, in the range 250336 to 305983 are for 1965. These Olympic Specials were made in the Gibson Kalamazoo plant alongside the Gibson Melody Maker, using the same woods and other materials. At least one of these guitars is in circulation with the ‘Melody Maker’ name in block white letters on the strip of pick guard just below the end of the fret board, although it is possible these might be a pick guard swap from a Gibson guitar or a Gibson spare replacement. It’s likely that these guitars were produced with the Epiphone brand, simply because at the time it allowed Gibson to expand its distribution by running two brands. 

Epiphone has used the ‘Olympic’ name for quite a number of models over the years and there may even be some confusion among enthusiasts over which Epiphone’s truly are ‘Olympic’ models. Currently the Olympic name seems to apply to a flat top acoustic Epiphone guitar. 

Around 1965, the Olympic was also made with a six on a side batwing headstock and a ‘Crestwood’ / ‘Wilshire’ body shape (a blockier more square body shape with a long upper horn). It seems as though Gibson standardised on the one shape for Epiphone guitars and simply fitted extra pickups, fancier binding / inlays and vibratos to differentiate between the models. This may have been so that none of the Epiphone branded guitars looked quite so much like guitars in the Gibson range, in this case the Melody maker. 

Body – This guitar has a one piece mahogany body (1 3/8 inches thick, same as a Gibson SG) in a dark brown to yellow vintage sunburst finish. The thin celluloid, faux tortoise shell, pick guard is attached with seven small, blackened steel, wood screws. The pick guard has shrunken slightly, pulling the screws out of vertical in their holes. The single coil pickup at the bridge has no height adjustment, it is simply bolted to the pick guard. The guitar has 250K log Volume and Tone controls fitted with push on Gibson gold ‘bell’ knobs with the silver anodised metal inserts. The tone capacitor is a disc ceramic.

Neck – 22 jumbo frets on a rosewood fretboard, one piece mahogany, set neck. Some visible fret wear on the first 3 frets under the plain strings. The back of the neck has numerous finish chips and dents. A lot of the finish in missing on the treble side between the nut and the ninth fret. Two of the ¼ inch mother of pearl fret markers (there are markers above the 3, 5, 7, 9, 12, 15, 17, 19 and 21 frets) are missing; one above the third fret and one of the pair above the twelfth fret. Side dots are 1/8 inch white plastic. The narrow headstock is black painted and parallel sided, with an “open book” crest. The Epiphone name is printed in gold along the centre of the headstock. 

Fitted with two, three-on-a-strip, Kluson nickel plated, pressed steel tuners with oval white plastic buttons. These are stamped DELUXE on the back of each tuner shell. These are not the original tuners, as marks from six individual tuners appear in the finish, concealed under the 3 on a side strips. Although strip Kluson tuners were used on the Olympic, so the current tuners are correct to the model and may in fact be the third set on this guitar (original strip Klusons changed for individual tuners, then the individual tuners changed for the existing Kluson strips).

A single action truss rod adjusts with a 5/16” hex nut at the headstock, access covered by a large black/white plastic laminate cover, secured by two screws. The neck joins the body at the 18th fret.

The guitar is fitted with a nickel plated wrap around bridge with a “lightning bolt” ridge and two grub screws to angle the bridge at the posts. This is original to the guitar and model. The ‘lightning’ ridge is compensated for a wound third string and in the 1960s the guitar would originally have shipped with a set of 0.012 gauge strings, with a wound third.

Re-strung with Ernie Ball 2215 Nickel Wound Electric Guitar Strings 10-52 Skinny Top Heavy Bottom.

Problems – In for cleaning (the guitar is quite grubby) and a light restoration. Dots at the third fret and twelfth fret are missing and are to be replaced. Straplock buttons to be replaced with ‘normal’ strap buttons. The two bell knobs are quite battered and the tone knob is no longer secure on the pot shaft. A fret rocker test shows frets: 6, 11, 13, 14, 16 and 21 are high.

Work done – Guitar cleaned and polished. High frets hammered and filed down until a fret rocker test shows they are level with the other frets. Fretboard and frets cleaned and polished. Missing dots replaced. New volume and tone knobs. New standard strap buttons fitted in place of the locking buttons. The middle two screws on each strip of 3 tuners were a poor fit and screwed in at an angle. Screw holes plugged and re-drilled.

Replaced the old ‘lightning ridge compensated for a wound third’ wrap over bridge with a Wilkinson adjustable intonation bridge. The volume and tone controls were sprayed with De-Oxit to reduce track noise and the shafts were lubricated with WD-40. A new set of EB 2215 strings fitted and the action and intonation adjusted and checked.

Intonation after re-stringing and setting the high and low Es as accurately as possible.

Low Error in cents

E +2

A 0

D 0

G +3

B 0

E 0


Parts – 


Ordered 2 sets of Ernie Ball 2215 strings £13.97 Strings Direct, one set for this guitar £6.98

2 black strap buttons and Gibson bell gold and silver knobs £11.80 from Axes R Us

Wilkinson wrap over bridge – £25 

Total – £43.78


Harley Benton PB-50 LH FR

Repair log: Harley Benton PB-50 LH FR (1950’s, Precision Bass, Left Handed in Fiesta Red) Vintage Series

Copyright retained, Terry Relph-Knight 20/06/18

Cost – £ 95.82 + shipping

Delivered with a black soft gig bag.

Fender do not currently make a single coil vintage precision bass in their standard range, let alone a left handed version. The closest is the Mike Dirnt Road Worn® Precision Bass® with a split humbucker pickup at £1,399.

A Fender 52 Precison Bass is only available from the Custom Shop.

The customer brought this bass to me because he wanted the headstock re-shaped from the Harley Benton outline to the correct shape for a Fender 50s Precision Bass.  

This bass is a Thomann in house brand, far east made, left handed version of the Fender 1951 Precision bass with the four pole single coil pickup and design features carried over from the Telecaster. It is a long scale instrument 864mm, 34 inches. It ships with D’Addario round wound strings 0.045, 0.065, 0.080, 0.100. Perhaps EXL170 ?, £22.99 of value just in the strings. 

This instrument represents astounding value for money. Like most low cost Chinese instruments it looks great and the paint finish is excellent, but there are signs of rapid finally assembly by semi-unskilled workers – the string tree barely attached by a very small screw at an odd angle, the untidy fit of the neck in the neck pocket and the neck screws fitted at odd angles.

Harley Benton PB-50 LH FR (1950’s

With just a little corrective work this bass is a unique looking instrument that plays well and sounds great.

Body – A basswood contoured body (probably in four or five pieces) in a Fiesta Red high gloss finish with a white vinyl single ply pick guard. Some of the countersinking for the pick guard attachment screws could be a little deeper. No neck shimming in the neck pocket. This body has forearm and belly contours and a fairly heavy edge radius, all of which the original 1951 instrument would not have had. 

Unlike the review of one of these basses on YouTube, this instrument does not have a hidden hole under the pickguard, the hole for the pickup lead is correctly drilled, from the pickup cavity through to the control cavity. Fair amount of dust under the pick guard. The control cavity is not screened.

Neck – A substantial modern C profile, two piece maple neck with a glued on 16 inch radius, 20 jumbo fret maple fret board (truss rod obviously routed and fitted from the front). Black plastic dot markers. Dual action truss rod adjusts at the headstock with a 4mm Hex key. Removed from the body the neck is almost flat with just a hint of forward bow. Rod had maybe 1 and ½ turns clockwise. White plastic 42mm nut. 4 bolt neck plate with a black plastic cushion. The four screws were very tight in their holes and had been drilled and fitted at odd angles. The corners of the heel are a bit sharp and the neck doesn’t fit all the way to the bottom of the neck pocket – there is about a 1mm gap.

Repair log: Harley Benton PB-50 LH FR

Hardware –  Pickup: Roswell VTN4 Vista Vintage PB Style single coil (specd. At 9Kohm DC resistance, actual DC resistance is 8.81K). Black Forbon flatwork, top printed with the Roswell logo in white, four ¼ inch Alnico 5 rod magnets, coil wrapped in black fabric tape.

L in HenrysQResistance

120Hz 4.114 0.3574 8.882

1000Hz 4.137 2.710 9.602

16mm Volume (B250K lin, 247.5K measured and treble A250K log, 257.6K measured) controls on a Tele prototype style chromed plate. Chromed dome knobs with plastic push on inserts. Wiring isn’t terrible. As this is left handed instrument the controls operate in reverse, so its anti-clockwise for more volume or treble. The linear volume is reasonably smooth but the log treble wired in reverse is of course, very on/off. The precision basses from the ‘50s had a 0.05uF (50nF) tone cap and today the nearest standard capacitor value would be a 0.047uf (47nF). The capacitor fitted is a 68nF nominal value plastic film capacitor which measures at 73.26nF. This larger value would also tend to exaggerate the on / of nature of the tone control.

The chromed 4 saddle bridge plate is probably a zinc alloy casting, but the barrel saddles are of chrome plated steel. 4 Kluson style elephant ear tuners with centre split posts. The tuner posts are steel, not zinc alloy, I don’t know if the chromed gear is cast zinc or brass. A single round string tree between the E and the A tuners. String tree screw is very small, is fitted at a weird angle, and barely bites into the headstock.

The strap buttons are rather notional – small and without much taper.

Problems / modifications – Customer wanted the Harley Benton headstock outline re-shaped to something closer to the original Telecaster shape. As became apparent, the Volume and Tone controls are unsuitable values and do not work well. The output jack is very cheap and flimsy.

Very poor intonation.

Work done – Disassembled the bass and checked for fit and finish. Deepened the pick guard screw countersinking a little, as a few of the screws were standing a little proud. Countersunk the screw holes in the body to minimise any possibility of finish cracking around the holes. Countersunk the screw holes in the neck to minimise tear out and ensure a flush fit to the bottom of the neck pocket.

Sanded a little more of a radius on to the corners and back of the heel to improve the neck fit.

Lubricated the four neck screws with candle wax so they aren’t quite so stiff to screw home.

Re-cut the outline of the headstock to be closer to a ‘53 precision bass, using a template for a Mike Dirnt signature bass. Sealed the cut surfaces with 3 coats of Danish oil. 

Plugged the string tree hole, re-drilled it and fitted a more robust screw. Fitted a matched pair of more robust screws to the jack plate. 

Replaced the volume and tone controls with Alpha 25mm 250K anti-logarithmic pots, the tone cap with a 0.047uF (46.22nF measured) plastic film capacitor and the output jack with a Switchcraft jack. Re-assembled and adjusted the intonation, which was way out. Also tweaked the action/saddle heights a little as the saddles were all at odd angles.

Intonation as delivered (now adjusted for zero error)

E +6

A +13

D +6

G +8

It doesn’t seem as though intonation was ever set on this instrument as it was a long way out. Probably the saddles were left in a what looked like a sensible stair step pattern as the bridge came off the factory pile. The saddle heights also don’t seem to have received much attention since all four are slightly tilted. 

As with most bass string sets the two low strings in the D’Addario set fitted are double wound while the two uppers are single wound. Consequently the intonation compensation for the two pairs of strings is almost the same, with the two single wound strings requiring a shorter string length than the two double wound. This explains why Leo Fender thought he could get away with only two saddles, each saddle sharing a pair of strings, for the original design of this bass. 

Action as delivered – open string action at the twelfth fret – G  2mm E 3mm

After adjustment G 2mm E 2.5mm

A fret rocker test did not reveal any high frets.


Repair Log: Roland Space Echo – Chorus Echo RE-301 SN: XXXXXX

Log last updated – 02/02/18

Copyright retained by Terry Relph-Knight

Value – £100,  They can be found for £155 in very good condition (which this one isn’t)

The Roland Space Echo RE-301 tape loop delay has a sound-on-sound playback head and three delay playback heads. It also has a built in BBD chorus and a spring reverb.

Note – The Roland user manual says – ‘Wow and flutter is minimised by the use of a free running system, which also serves to extend tape life over 300 hours.’ So tape loops still need to be changed relatively frequently.

After a lot of investigation it looks very much as though this unit has been patched together out of two or more broken RE-301s and possibly further ‘repairs’ have been carried out over the period it has been in use.

Front panel controls are –

Metering – Peak level LED, MC VU meter

Input mixer – 3 x Input level rotary controls, -20 -35 -50dB slide switch and three ¼ inch input jacks.

Direct signal on/off slide switch – Switches between Wet and Dry mixed or Wet/effect only.

Chorus – Intensity control, indicator LED, Chorus on/off via push button or remote jack

Echo – Indicator LED, Echo on/off via push button or remote jack, 6 way mode switch for playback head selection, Sound-on Sound toggle and remote jack, volume, repeat rate (with a remote jack) and intensity controls, a toggle switch allows switching to single delay regardless of the setting of the intensity (regeneration) control. At some point this switch has been replaced with a three way centre off switch.

Reverb – Volume control

Output – Bass and Treble controls, -15,-25,-35 dB three way level slide switch, A (A+B) and B output jacks.

Power toggle switch, VU meter illuminates when power is on.

Head order (left to right)

Sound on sound PH4, Erase head, Record Head, PH1/Mode1, PH2/Mode2, PH3/Mode3

(Visually the azimuth on S on S, PH2 and PH3 looks off).

Problems – In just for a general check over and alignment. The electronics seem very temperamental, it seems to act differently every time it is turned on. For example on one occasion echo modes 3,5 and 6 passed little signal with lots of hum. One another occasion, when first powered up the regeneration did not work, then with some control fiddling it came to life. The Chorus makes a sort of on/off gargling sound. The spring reverb just hums. Even switched off the RE-301 hums when plugged in to an amplifier indicating a ground problem somewhere.


Periodically the tape slips so the echo produced is not constant and regular. I now think this is entirely down to the tape loop. Even though the MTE replacement loops I bought are supposedly manufactured for the Space Echo I don’t think they are of good enough quality.

Work done

All but one of the original M3 thumb nuts (supplemented by one ordinary M3 nut) that secure the acrylic plate over the tape loop bin where missing. These were replaced with 5 stainless steel M3 thumb nuts.

Dirt and old tape oxide were cleaned from the tape bin, the head plate and the top surface of the unit. The two felt tape pressure pads were cleaned of dirt and oxide. The pinch roller was removed, cleaned with isopropyl alcohol, the centre bearing lubricated and the roller replaced. NOTE – All rollers and pads now replaced.

The hard rubber pinch roller has a sintered bronze sleeve bearing mounting onto a polished steel shaft. It is secured by an M3 screw that has a small spring washer, a larger plain washer and then there is a felt ring to capture any excess oil. The screw and washers are concealed under a black rubber mushroom push-on cap. The head of the M3 cross head screw holding the pinch roller was quite chewed up so this was replaced with an M3, stainless steel, hex button head screw.

The feed roller bearing on the other side of the tape path was removed cleaned and lubricated (now replaced). The feed roller is held in place by an M3 12mm countersunk cross head screw that passes through an aluminium disc and a nylon spacer that fits in the centre of the ball race bearing used as the feed roller. The ball race bearing is spaced top and bottom by a thin bronze washer.


A new tape was loaded and then the bias trap was adjusted for maximum rejection and the bias level set. All the heads where cleaned with isopropyl alcohol, magnetically degaussed and were checked and adjusted for height and azimuth.

Replaced the VU meter 12V pea lamp with a wide angle white LED fed from an 820ohm resistor.

Unplugged all 16 internal Molex connectors, wiped the contact pins with DeOxit and plugged all the connectors back in.

To fix general hum problems I removed the step down auto-transformer from inside the case and re-wired the echo unit with a long mains lead terminated in the US 110V mains plug. This can now plug in to the auto-transformer sited outside the case.

Glued down all the pealing edges of the Tolex around the wooden case where the original adhesive had failed.

Further problems With the MTE RT-1L tape loaded the unit developed tape slip resulting in pitch wobble. As the only reliable source of Space Echo parts I ordered two service kits from in Australia. The original order went missing somewhere between the sorting office and my house. EchoFix sent me another set for the cost of postage. I also paid a customs charge on the original shipment.

Each kit contains a new pinch roller, feed roller, a set of friction felts and two replacement tapes. Having fitted all these parts the tape slip problem seems to be solved.

I re-set the bias trap, re-biased for the new tape and checked all the head azimuths. Note – playback from head 3 seems to be half that from the other two heads. There do seem to be level adjustment presets on the main PCB, but I did not adjust them.

Fitted a new TA7200P integrated power amp in an effort to get the reverb to work. Nope sadly not, although the chorus has come back to life.


This unit has either been ‘pragmatically’ repaired, or is a Frankenstein. An etched aluminium plate screwed to the back of the case clearly states it to be a 220V AC unit and indeed it does run on UK mains. However an internal examination shows that a  240V to 110V conversion auto-transformer, supplied by the UK electrical chain Ryness, has been fitted inside the case. This is fed by the external mains cable and the Roland power transformer (which must have a 120V primary – it does, the primary wire colours match those for a 120V supply as shown in the Roland service manual) is plugged in to the output socket of this extra transformer with a large yellow US three pin plug that mates with a socket on the side of the extra transformer.

Either this unit has been cobbled together from a US and a European unit, or the original Roland 220V mains transformer blew and was replaced with an original 110V transformer, making it necessary to add the extra conversion auto-transformer. Which by the way has input neutral (now blue) wired to the right (white, which is US neutral) on the US plug. US live is black and is on the left looking in to the socket. The actual Roland power transformer fitted inside the unit is definitely the transformer designed for 110V input because it has the white (neutral) and green/blue (live ,fused) input wires as specified on the Roland circuit in the service manual. A 240V unit should have a Roland transformer with red (250V), brown (230V) and white (neutral) as the primary wires. The Roland transformer is connected the wrong way round – the green/blue wire should go to the internal fuse.

In any case this extra transformer is mounted right next to the built-in spring reverb tank at the output end of the tank. As a result the reverb hums because the output picks up the field of the transformer.

The spring tank itself had been moved to the right to make room for the auto-transformer and one of the support brackets that holds the case together removed to make room for the tank. The spring tank is an interesting design, an OC Electronics Folded Line Reverberation Device Type 60, apparently “Manufactured by beautiful girls in Milton, Wisconsin under controlled atmospheric conditions” with a folded Z configuration of three springs. The drive and pickup coils are sited at the ends of the Z with the angles supported on resilient mounts. Unfortunately the drive signal for the reverb seems to have gone AWOL, there is audible spring clang if you tap the tank, but no reverb effect. Connecting a 3V light bulb continuity tester briefly across the input coil also produces a crash so the input coil is intact and the delay tank seems to be working. Either the reverb drive amplifier no longer works, or it is not receiving an input signal. The reverb drive chip is a TA7200P, a 3.3W single chip audio power amp in a 10pin SIL package. EBAY £3.08.

The chorus only makes some rather weak wobbling sounds. Adjusting the BBD clock balance and BBD bias trimmers does not bring the clock signal close to the symmetry shown in the service manual. The chorus delay is produced by a MN3004, a 512 stage Bucket Brigade Delay chip in a 14 pin DIL package. These can just about be found on EBAY for £50.

Pilot / VU meter filament pea bulb has blown (has previously been replaced by splicing the wires). Voltage is 13.45V DC. Replaced with a wide angle white LED 30mA max 3.1V drop. 10V 20mA = 560 ohms, hmm I have 820 ohms to hand I’ll use that, seems bright enough.

Unreliable operation – There are 16, Molex 0.15pitch SIL connectors, 5 on the power and bias board and 11 on the main PCB. It appears that these have been unplugged and re-plugged several times in the past and is very possible that these aren’t all making reliable contact. Also the echo mode switch seems very uncertain in its operation. Unfortunately this is a sealed switch.

Power supply

The power supply is in two sections – a bipolar +14.5V, -14.5V to feed the op-amps and other electronics and a supply for the variable speed servo motor. Pin 1 of IC4 / R406 is labelled – 13.3V (fast) to – 5.5V (slow).

Measured supply voltages are now –

Measured supplies –   Minus 13.91V Plus 14.04V

Servo at Pin 1 of IC4 – 6.33 to 12.53V

Basic functionality tests from input to output

All three input mixer channels work and behave identically. The level controls function, the level switches work (there are internal pre-sets to balance the input gains VR15, VR16, VR17). The peak LED and VU indicate as expected.

The Direct signal switch switches the mix of the direct signal on and off. With all the effects off the clean signal sounds reasonably free of hum and noise and is relatively undistorted. The mixed output with the Direct switch on appears on the A+B jack, the B jack is always effect only.

With Direct off and Chorus on the output is vibrato only.

The Chorus switch does switch in an effect, but rather than a smooth swirling chorus, there is a two step phase change sound. It may just be that the chorus circuit trimmers (VR12 BBD bias, VR13 BBD clock balance) need attention or it may be a general power supply problem (having cleaned all the connectors, cleaned the back of the PCB of dirt and flux and set the two trimmers to their centre positions the chorus now seems to have come back to life).

The Echo mode switch results in an audible delay although not particularly prominent delay on positions 1,2 and 4. There is a strong hum and little signal on positions 3,5 and 6. According to the cheat sheet on the lid “Echo rate decreases in the order of 1-2-3. Positions 4-5-6 give you soft echo with complex effect”. From the circuit diagram modes 1,2 and 3 select either playback head 1,2 or 3 through JFET switches. Using a simple diode matrix, modes 4,5 and 6 select either 1+2, 2+3 or 1+2+3. So any mode that involves switching Playback 3 is compromised. Either playback channel 3 (head and or pre-amp) is compromised or the switching voltage or JFET is dead.

Echo Intensity easily goes into echo feedback (VR18 sets the intensity limit).

The spring reverb hums because of the proximity of the step down transformer.

The output tone controls and the output level switch seem to work and the A+B and B jacks output signal as expected.

Sound on sound produces a strong signal (SonS level is VR14).

Either this unit has a power rail problem, or all the presets have drifted a long way, or someone has been inside and fiddled with all the presets without knowing what each one does.

Parts ordered – I ordered two Service Kits for the RE-101,201,301,150 at 110 AUD each (£67.41) on the 18/08/17 (around then anyway)

Paid a customs charge on 07/09/17 of £ 32.69

Ordered a TA7200P from Ebay 8.40 Euro paid by PayPal 07/09/17.

Parts –

5 x Stainless steel thumb wheel nuts £ 3.99

1 x high intensity LED to replace the incandescent pilot light £ 00.50

2 x service kits – from Visa 21/08/17 £123.62 + £3.70 fee = £127.32

Customs charge £32.69 – from Visa 08/08/17 £32.69

Postage for the second set of kits – from PayPal 28/09/17 AU $ 23.70 £14.47

Space Echoes – Invoiced to date – 2007240 18/03/17 RE-150 Space Echo £68

Invoice for this RE-301 – 2007275

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